text: The common features of Fisher carbenes are:
  * low oxidation state metal center
  * middle and late transition metals Fe(0), Mo(0), Cr(0)
  * π-acceptor metal ligands
  * π-donor substituents on the carbene atom such as alkoxy and alkylated amino groups.
  Examples include  and .
  Fisher carbene complexes are related to the singlet form of carbenes, where both electrons occupy the same sp orbital at the carbon. This lone pair donates to a metal-based empty d orbital, forming a σ bond. π-backbonding from a filled metal d orbital to the empty p orbital of the carbon atom is possible. However this interaction is generally weak since the alpha donor atoms also donate to this orbital. As such, fisher carbenes are characterized as having partial double bond character. The major resonance structures of Fisher carbenes put the negative charge on the metal centre, and the positive on the carbon atom, making it electrophilic. 
  Fischer carbenes can be likened to ketones, with the carbene carbon atom being electrophilic, like the carbonyl carbon atom of a ketone. This can be seen from the resonance structures, where there is a significant contribution from the structure bearing a positive carbon centre. Like ketones, Fischer carbene species can undergo aldol-like reactions. The hydrogen atoms attached to the carbon atom α to the carbene carbon atom are acidic, and can be deprotonated by a base such as n-butyllithium, to give a nucleophile, which can undergo further reaction.